Method of manufacturing an article having a cylindrical peripheral wall and integral thin-walled portions inwardly thereof

ABSTRACT

A method of manufacturing at once an article having a cylindrical peripheral wall and integral thin-walled portions inwardly thereof from a circular blank of a sheet material with a single stroke of pressing operation. In the first part of the stroke, the blank is subjected to a rearward extrusion to form the blank into a semi-finished article having the peripheral wall and the thin-walled portions with a thin bottom wall being left with the semi-finished article. In the remaining part of the stroke, the bottom wall is punched out of the semi-finished article to thereby provide a finished article.

United States Patent Hashimoto et al.

METHOD OF MANUFACTURING AN ARTICLE HAVING A CYLINDRICAL PERIPHERAL WALL AND INTEGRAL THIN-WALLED PORTIONS INWARDLY THEREOF Inventors: Seiya Hashimoto, Tokyo; Soji Takahashi, Kodaira; Yasuhiro Hattori, Tokyo; Kuninori Imai, Hachioji, all of Japan Assignee: Hitachi, Ltd., Tokyo, Japan Filed: April 7, 1971 Appl. No.: 131,893

Foreign Application Priority Data April 10, 1970 I Japan ..45/30188 US. Cl. ..72/254, 72/267, 72/334, 72/354 Int. Cl. ..B2lc 23/20 Field of Search ..72/334, 356, 359, 354, 267, 72/254, 255; 29/DIG. 9, 25.17, 25.18; 313/356; 76/107 S [56] References Cited UNITED STATES PATENTS 1,482,697 2/1924 Orr ..72/255 FOREIGN PATENTS OR APPLICATIONS 677,779 8/1952 Great Britain ..72/267 Primary Examiner-Richard J. Herbst Attorney-Craig, Antonelli & Hill [57] ABSTRACT A method of manufacturing at once an article having a cylindrical peripheral wall and integral thin-walled portions inwardly thereof from a circular blank of a sheet material with a single stroke of pressing operation. In the first part of the stroke, the blank is subjected to a rearward extrusion to form the blank into a semi-finished article having the peripheral wall and the thin-walled portions with a thin bottom wall being left with the semi-finished article. In the remaining part of the stroke, the bottom wall is punched out of the semi-finished article to thereby provide a finished article.

4 Claims, 22 Drawing Figures PATENTEB "AR 61973 SHEET 10F 6 FIG.

INVENTORS SEN HHSHHWOTO SOS\ THKHHRSHI Kama-R0 HQTTOFQ a K NINQRQ \Mm BY Cholg, QM 8r mush ATTORNEYS PATENTEDMAR 6 I915 3,719,068

SHEET 5 OF 6 INVENTORS BY CW awn; V FNLQQ ATTORNEYS METHOD OF MANUFACTURING AN ARTICLE HAVING A CYLINDRICAL PERIPHERAL WALL AND INTEGRAL THIN-WALLED PORTIONS INWARDLY THEREOF BACKGROUND OF THE INVENTION Field of the Invention The present invention relates generally to a method of manufacturing an article having a peripheral wall and integral thin-walled portions inwardly thereof and, particularly, to a method of manufacturing an article having a cylindrical peripheral wall and a plurality of partitions integral with the peripheral wall and extending radially inwardly from the inner surface of the peripheral wall toward the axis thereof, such as, for example, an anode of split anode magnetron.

As an example, an anode of split anode magnetron has a cylindrical peripheral wall and a plurality of partitions or vanes extending radially inwardly from the inner surface of the peripheral wall toward the axis thereof, each vane having a smaller ratio of lateral width relative to height. The vanes define a plurality of resonance cavities between respective adjacent pairs of the vanes. The inner ends of the vanes define a circular central opening for receiving a cathode. The anode is usually made of oxygen free copper.

The oscillation frequency of a magnetron is directly influenced by the dimensional accuracy of the resonance cavities of the anode. In the manufacture of the anode of a magnetron, therefore, it is required that the vanes are worked 'with great preciseness with respect to the dimension and mutual positioning of the vanes.

It is very troublesome to produce, by usual cutting operation, an article of such a complicated configuration. It is practically impossible to apply such usual cutting operation to the mass-production of small-sized articles each having such. a complicated configuration and requiring higher preciseness in dimension and shape.

For the reasons, a so-called brazing process has heretofore been employed to manufacture magnetron anodes. With this process, a cylindrical part and a set of a plurality of plate-like parts are separately pre-formed and thereafter these parts are assembled and secured together to form a magnetron anode. This process requires that individual plate-like parts are secured to the cylindrical part by means of brazing. For this reason, the assembling operationv not only requires complicated and troublesome workbut also fails to provide a satisfactory accuracy of the assembled -or finished product. 7 v

There has also been employed another method which is carried out by virtue of punching. With this method, a cylindrical punch is forced into a circular blank of a thick sheet of copper at a central zone thereof. The punch is providedwith slits or-grooves at the positions corresponding tothose of the vanes of a desired magnetron anode. The grooves are each complementary in shape and size to the vanes of the anode so that a punching operation removes those portions of the blank which correspond to a central opening and resonance cavities of the anode. With this'method, it can be expected that operation is extremely simplified because the peripheral wall and vanes are formed at once from a single piece of blank. This method, however, falls in short of satisfaction in that the method provides a reduced accuracy of manufacture when each of the vanes has a small ratio of the lateral width of the vane with respect to the height thereof. In fact, it is almost impossible to apply this method to a case in which the ratio of the lateral width of a vane relative to the height thereof is less than one third (Va).

While the above discussion is directed to the problems in the conventional methods of manufacturing magnetron anodes, these problems are encountered not only in the manufacture of a magnetron anode but also in the production of any other similar article having a peripheral wall and integral thin-walled portions of small ratio of lateral width relative to height and disposed inwardly of the peripheral wall.

SUMMARY OF THE INVENTION It is a principal object of the present invention to eliminate the problems in the prior art methods of manufacturing articles of the class specified in the above.

It is another object of the present invention to provide an improved and unique method which enables to manufacture, by a simplified operation and with an increased preciseness, an article having a peripheral wall and integral thin-walled portions of a small ratio of lateral width relative to height and disposed inwardly of the peripheral wall.

The above objects may be achieved by the method of the present invention in which a blank of a sheet material is successively subjected to extrusion and shearing with a single stroke of pressing operation to provide at once a finished product of a desired shape.

More particularly, the method of the present invention causes a punch to be forced into a blank of a sheet material in a first part of the stroke of pressing operation to subject the blank to a rearward extrusion which forms a semi-finished article having a peripheral wall and thin-walled portions with a thin bottom wall being left with the semi-finished article. In the second or remaining part of the stroke, the bottom wall is subjected to a shearing by which the bottom wall is punched out or removed away from the semi-finished article to thereby provide a completed or finished article.

Further objects, features and advantages of the present invention will become apparent from the following description ofa preferred embodiment of the invention with reference to the accompanying drawings.

DESCRIPTION OF DRAWINGS FIG. 1A is a top plan view of a magnetron anode manufactured by an embodiment of the method according to the present invention;

FIG. 1B is an axial section taken along line II in FIG. 1A;

FIGS. 2A to 2C illustrate in axial sections a work piece in respective steps of the method of the present invention;

FIGS. 2A to 2C are top plan views of the work piece in the respective steps of method shown in FIGS. 2A to 2C, respectively;

FIG. 3 is a fragmentary axial sectional view of an apparatus employed in carrying out the method of the present invention;

FIGS 4A to 4C are fragmentary axial sectional views of the apparatus in different positions corresponding to the steps of the method shown in FIGS. 2A to 2C, respectively;

FIG. 5A is a side elevational view of the upper punch of the apparatus shown in FIG. 3 with a part of the punch being shown in longitudinal section;

FIG. 5B is a cross-sectional view taken along line V-V in FIG. 5A;

FIG. 6A is a side elevational view of the lower punch of the apparatus shown in FIG. 3 with a part of the punch being shown in longitudinal section;

FIG. 6B is a cross-sectional view taken along line Vl-VI in FIG. 6A;

' FIGS. 7A and 7B are top plan and axial sectional views, respectively, of the extruding die of the apparatus shown in FIG. 3;

FIG. 8A is a top plan view of the punching die of the apparatus shown in FIG. 3;

FIG. 8B is an axial sectional view taken along line VIII-VIII in FIG. 8A; and

FIGS. 9A and 9B illustrate in top plan and side elevational views, respectively, the shape of the material punched out of the workpiece by a shearing step.

DESCRIPTION OF A PREFERRED EMBODIMENT A description will be made with respect to an embodiment of the present invention which is applied to the production of a magnetron anode having a cylindrical peripheral wall 1 and a plurality of vanes 2 radially inwardly extending from the wall 1 to define resonance cavities 3 and a circular central opening 4, as shown in FIG. 1.

FIGS. 2A to 2C illustrate respective steps of the production of the magneton anode 1, shown in FIG. 1, according to the method of the present invention, FIGS. 2A and 2A showing a circular workpiece or blank 4 of copper, FIGS. 28 and 28 showing a semiprocessed or semi-finished article b obtained after a rearwardly extruding step, and FIGS. 2C and 2C showing a finished product c obtained after a shearing step. As will be appreciated from the illustrations in these figures, the method of the present invention comprises a steps of subjecting the blank a to a rearward extrusion to obtain the semi-finished article b having a cylindrical wall 1, a plurality of vanes 2 and a thin-walled bottom 5 (FIGS. 28 and 2B), and a step of subjecting the semifinished article b to a shearing to remove the bottom wall 5 for obtaining the finished product c (FIGS. 2C and 2C). With the method of the present invention, the above-stated two steps are carried out in succession in a single stroke of a press, as will be described in more detail later.

FIG. 3 illustrates an essential part of the apparatus employed in carrying out the afore-described method of the present invention with the apparatus being shown as being loaded with a piece ofa copper blank a. As will be seen in this figure, the apparatus includes an upper punch 11, lower punch 12, a die 13 for use in extrusion step (hereinunder termed extrusion die") and another die 14 for use in punching operation (hereinunder termed punching die). The apparatus also includes a support 15 for axially supporting the dies 13 and 14, and a frame member 16 for radially holding the dies 13 and 14. The blank a is placed within the die 13 and on the upper face of the die 14.

Referring now to FIGS. 5A and 5B, the upper punch 11 has a stem 11f of a diameter substantially the same as the outer diameter of the cylindrical peripheral wall 1 of a magnetron anode to be produced, a lower portion lle of a diameter substantially the same as the inner diameter of the peripheral wall 1 of the magnetron anode, and a shoulder portion 11d defined between the stem 11f and the lower portion lle. The latter is formed with a plurality of radially and axially extending slits or grooves 111; for forming the vanes 2 of the magnetron anode. For this purpose, the grooves 11b are complementary in shape and size to the vanes 2, respectively. Between each adjacent pair of the grooves 11b, there is defined a tooth which also is complementary in shape and size to a resonance cavity 3 in a magnetron anode. Moreover, a boss 11a is defined by the radially inner ends of the grooves 11b, the boss being integral with the teeth 11c and being complementary in shape and size to the circular central opening 4 in the magnetron anode. Preferably, the lower portion He has its height or axial dimension which is equal to or slightly larger than the height or axial thickness of the peripheral wall 1 of the magnetron anode.

As will be seen in FIGS. 6A and 6B, the lower punch 12 has its outer diameter which is substantially the same as the inner diameter of the peripheral wall 1. The lower punch is also formed in the upper part thereof with a plurality of radially inwardly and axially extending slits or grooves 12b at the positions corresponding to the vanes 2 of the magnetron anode. The grooves 12b are complementary in shape and size to the vanes 2, rexpectively, and define a plurality of teeth 12c, each being complementary in shape and size to a resonance cavity 4 in the magnetron anode, and a central boss which is also complementary in shape and size to the circular central opening 4 in the magnetron anode, as is in the case of the upper punch 1 1.

Referring then to FIGS. 7A and 7B, the extrusion die 13 comprises an annular ring of a relatively larger wall thickness defining a circular axial central hole 13a of a diameter which is substantially the same as the outer diameter of the peripheral wall 1 of the magnetron anode.

As shown in FIGS. 8A and 8B, the punching die 14 comprises a cylindrical peripheral wall 14d of a relatively larger thickness having an inner diameter substantially the same as the inner diameter of the peripheral wall 1 of the magnetron anode, and a plu rality of cutting or shearing teeth 14b extending radially inwardly from the upper end portion of the peripheral wall 14d. The shearing teeth 14b are substantially identical in shape and size to the vanes 2 of the magnetron anode, respectively, and cooperate together to define a plurality of fan-shaped spaces 14c and a circular central opening 14a, each space and the central opening 140 being substantially identical in shape and size in plan view with a resonance cavity 3 and thecentral opening 4 of the magnetron anode, respectively.

The lowerupunch 12 and the punching die 14 are shaped and dimensioned relative to one another such that, when the punch 12 is moved upwardly into the die 14, the shearing teeth 14b of the latter are snugly received in the grooves 12 of the punch 12 and the spaces 14a and 140 of the die 14 are completely filled with the central boss 12a and the teeth 12c of the punch 12, respectively, with the top faces of the boss 12a and the teeth 12c of the punch 12 and the shearing teeth 14b of the die 14 forming a continuous plane, as will be seen in FIG. 3.

FIGS. 4A to 4C illustrate the operation of the abovedescribed apparatus. Namely, FIG. 4A illustrates the apparatus in a position in which a blank a has just been placed in position. FIG. 48 illustrates the next position of the apparatus in which the upper punch 11 has been forced to mode downwardly to perform a required extrusion so that a semi-finished article b has been formed. FIG. 4C illustrates a further position of the apparatus in which the upper punch 11 has been further moved downwardly and the lower punch 12 has been retracted downwardly to perform a shearing of the bottom wall 5 of the semi-finished article b with a result that a finished product c has been obtained.

The successive steps of the process will be described hereunder in more detail. First of all, a circular workpiece or blank is provided. The blank a is coated at the peripheral surface with an appropriate lubricant such as, for example, molybdenum disulfide in pastelike form. Then, the blank a is placed within the die 13 and on the geral surface provided by the lower punch 12 and the die 14, as shown in FIG. 4A. The upper punch 11 is then forced to move downwardly with the lower punch 12 being restrained from being moved downwardly for thereby subjecting the blank to a rearward extrusion. More specifically, the downward movement of the upper punch 11 into the blank causes a generally rearward plastic flow of the material of the blank into a generally annular space defined between the lower portion lle of the upper punch 11 and the die 13 and into the grooves 11b in the punch 11 so that a semi-finished article b having a cylindrical peripheral wall 1 and vanes 2 is formed (FIG. 4B). This rearward extrusion is completed while there is left with the semifinished article b a bottom wall 5 of a thickness substantially the same as the lateral width or circumpherential dimension of each vane 2. The lower punch 12 is then released from the restraint so that the continued downward movement of the upper punch 11 punches the bottom wall 5 to provide a finished product 0. The mass of the bottom wall 5 thus punched out of the semi- For this purpose, any conventional locking mechanism may be employed to lock the lower punch 12 in the position shown in FIGS. 4A and 48 during the extrusion step. The punch 12 may be unlocked when the process is reached by the transition to the next punching or shearing step. The timing of the transition of the process to the shearing step may be determined by detecting the pressure for moving down the upper punch 11 arriving at the maximum pressure value Pm. Alternatively, the timing of the transition may be determined by detecting the distance, over which the upper punch 11 is to be moved down, arriving at a predeterfinished article b has a shape as shown in FIGS. 9A and 1 9B and comprises a central portion 5a which has left a central circular opening 4 with the finished product c or magnetron anode, and a plurality of fan-shaped portions 5c which have left resonance cavities 3 with the product c. The fan-shaped portions define together slits 5b which have left vanes 2 with the product 0.

As the upper punch 11 is brought into intimate meshing engagement with the punching die 14 after the bottom wall 5 has been punched out, the finished product c is confined within a closed space defined by the upper punch 11 and the dies 13 and 14. Thus, when the upper punch 11 is further forced to move downwardly, the finished product 0 may be press-shaped.

In order that the afore-described extrusion and shearing steps may be carried out in succession, the lower punch 12 should be restrained from being moved or retracted downwardly during the extruding step. Then, the punch 12 should be released from the restraint at the transition to the shearing step so that the punch 12 may be retracted during the shearing step.

mined value at which the extrusion step should be transferred to a shearing step.

In a further modification, a strong spring may be employed to upwardly bias the lower punch 12 so that, when a predetermined extrusion is completed (that is, when the pressure on the upper punch 11 required for the downward movement thereof arrives at the maximum pressure value Pm for the extrusion), the downward force exerted on the lower punch 12 first overcomes the upward biasing force from the spring to force the lower punch 12 to be moved downwardly.

In a still further modification, an appropriate hydraulic mechanism may be employed to exert an upward force P2 to the lower punch 12 and may be so controlled that the upward force P2 be in such a relationship as being shown in FIGS. 4A to 4C with respect to the downward force P1. In carrying out the method of the invention by use of such hydraulic mechanism, it will be most convenient to predetermine the relationship between upward and downward pressures such that P1 is equal to P2 during extrusion step and P is equal to zero (0) when the pressure Pl required for the extrusion exceeds a predetermined maximum value Pm. Alternatively, the pressure P2 may be maintained equal to Pm during the extrusion step may be made equal to zero (0) when the pressure P1 exceeds the pressure Pm.

Lastly, the production of the magnetron anode shown in FIG. 1 will be described hereunder with reference to a dimensional example. When a required magnetron anode has its following dimensions:

Outer diameter of peripheral wall 1 46.0 mm Inner diameter of peripheral wall I 40.0 mm Height of peripheral wall I 10.0 mm Lateral width of vane 2 1.6 mm Diameter of central opening 4 l0.0 mm,

it has been found that appropriate dimensions for a blank 0 for the magnetron anode are as follows:

Diameter Thickness With this example, the upper punch 11 has a downward movement of about 3.4 mm with downward pressure of I50 tons with a result that a semi-finished article b has a peripheral wall 1 of 10.0 mm in height or axial dimension and a bottom wall 5 of 2.1 mm in thickness. It has been found that any further increase in the downward pressure on the upper punch 11 is hardly be able to further proceed with the extrusion. Stated in other words, the extruding operation alone is insufficient to punch the bottom wall 5.

With the present invention, when this state attains, the upward pressure force is removed from the lower punch 12 so that the same is allowed to be moved or retracted downwardly to bring the process into a transition to a next step of subjecting the bottom wall to shearing. Thus, the upper punch ll is immediately moved downwardly until the bottom face of the upper punch 11 is reached by the top face of the punching die 14 so that the above-mentioned bottom wall 5 of 2.1 mm thickness is punched out of the semi-finished article b. As each of the vanes 2 thus left with the product 0 has a ratio of its lateral width at its bottom face relative to the height which ratio is 0.8, the punching operation does not decrease the accuracy in the dimension of the vanes 2. When the punching step is completed, the upper end faces of the peripheral wall 1 and the vanes 2 formed by the rearward extrusion are subjected to a shaping or flattening by the flat surface of the shoulder 11d of the upper punch to thereby provide a finished product or magnetron anode.

Although the above description has been made in connection with an embodiment of the invention which is directed to the manufacture of a magnetron anode, the scope of the present invention is not limited to the described and illustrated embodiment and it is to be understood that the invention may be generally applied to the manufacture of any other article having a peripheral wall and integral thin-walled portions extending inwardly therefrom.

The method of the present invention provides the following advantages:

1. Operation is remarkably simplified in that an article of a complicated configuration, such as a magnetron anode, for example, can be manufactured at once with only a single stroke of pressing operation;

2. Since the extruding step and the shearing or punching step are carried out in succession with a single apparatus, there is no possibility that any displacement or offset takes place between the respective steps, with a result that a product of higher quality is obtainable;

3. Since the extruding step performs substantial part of the process of manufacture, the bottom wall to be punched can have a reduced thickness, solving the problem of the ratio of lateral width relative to height, and minimizing loss of material; and

4. Therefore, mass-production may be carried out at greatly reduced cost of manufacture.

For the above reasons, the present invention provides greater industrial advantages when applied to the manufacture of an article having a peripheral wall and a plurality of integral thin-walled portions extending inwardly therefrom, such as a magnetron anode, for example.

We claim:

1. A method of manufacturing by a pressing operation an article having a cylindrical peripheral wall and integral thin-walled portions inwardly thereof, said method comprising the steps of, in a first portion of a single stroke of the pressing operation, rearward-extruding a blank of a circular sheet material by means of a both opened ended female die and a male die comprising one punch formed with a plurality of radially extending grooves and the other punch formed with the same grooves as said one punch, to form a semifinished article having a cylindrical peripheral wall with a plurality of thin-walled portions on its inner surface corresponding to the grooves of said male punch and a thin bottom wall connected with one end of said peripheral wall and integrally with said thin-walled portions, and, in a second portion of the single stroke of the pressing operation, subjecting said bottom wall to a precise shearing to cause the same to be punched out of said semifinished article in succession to said rearward-extruding step in the single stroke of the pressing operation.

2. A method of manufacturing by a pressing operation a magnetron anode, said method comprising the steps of, in a first portion of a single stroke of the pressing operation, rearward-extruding a blank of a circular sheet of copper by means of a both opened ended female die and a male die comprising one punch formed with a plurality of radially and axially extending grooves and the other punch formed with the same grooves as said one punch, to form a semifinished article having a cylindrical peripheral wall with a plurality of thin-walled portions on its inner surface corresponding to the grooves of said male punch and a thin bottom wall connected with one end of said peripheral wall and integrally with said thin-walled portions, and, in a second portion of the single stroke of the pressing operation, subjecting said bottom wall to a precise shearing to cause the same to be punched out of said semifinished article whereby said semifinished article is punched out, being sandwiched between said one punch and said other punch in succession to said rearward-extruding step in the single stroke of the pressing operation.

3. A method of manufacturing by a pressing operation an article having a cylindrical peripheral wall and integral thin-walled portions inwardly thereof, said method comprising the steps of initially driving a punch means in a first direction against a blank of circular sheet material arranged in die means to rearwardly extrude the blank and form a semifinished article having a cylindrical peripheral wall with a plurality of thinwalled portions on its inner surface and a thin bottom wall integrally connected with the peripheral wall and the thin-walled portions, and then driving the punch means in the first direction against the semifinished article for subjecting the bottom wall to shearing and punching the bottom wall from the semifinished article such that a finished article having a peripheral wall and integral thin-walled portions inwardly thereofis formed in a single stroke of the pressing operation.

4. A method according to claim 3, wherein the blank is copper and is arranged in two open ended dies, the punch means includes a first punch formed with a plurality of radially and axially extending grooves and another punch formed with the same grooves as the first punch, further including the steps of positioning the first and second punches in facing relation for cooperation with the dies, driving the first punch toward the second punch while maintaining the second punch in a first position with respect to the dies for rearwardly extruding the blank to form the semifinished article, then driving the first punch means towards the second punch and permitting the second punch to move in the same direction as the first punch to subject the semifinished article to shearing to punch the bottom wall which is sandwiched between the first and second punches from the semifinished article to operation. 

1. A mEthod of manufacturing by a pressing operation an article having a cylindrical peripheral wall and integral thin-walled portions inwardly thereof, said method comprising the steps of, in a first portion of a single stroke of the pressing operation, rearward-extruding a blank of a circular sheet material by means of a both opened ended female die and a male die comprising one punch formed with a plurality of radially extending grooves and the other punch formed with the same grooves as said one punch, to form a semifinished article having a cylindrical peripheral wall with a plurality of thin-walled portions on its inner surface corresponding to the grooves of said male punch and a thin bottom wall connected with one end of said peripheral wall and integrally with said thin-walled portions, and, in a second portion of the single stroke of the pressing operation, subjecting said bottom wall to a precise shearing to cause the same to be punched out of said semifinished article in succession to said rearward-extruding step in the single stroke of the pressing operation.
 1. A mEthod of manufacturing by a pressing operation an article having a cylindrical peripheral wall and integral thin-walled portions inwardly thereof, said method comprising the steps of, in a first portion of a single stroke of the pressing operation, rearward-extruding a blank of a circular sheet material by means of a both opened ended female die and a male die comprising one punch formed with a plurality of radially extending grooves and the other punch formed with the same grooves as said one punch, to form a semifinished article having a cylindrical peripheral wall with a plurality of thin-walled portions on its inner surface corresponding to the grooves of said male punch and a thin bottom wall connected with one end of said peripheral wall and integrally with said thin-walled portions, and, in a second portion of the single stroke of the pressing operation, subjecting said bottom wall to a precise shearing to cause the same to be punched out of said semifinished article in succession to said rearward-extruding step in the single stroke of the pressing operation.
 2. A method of manufacturing by a pressing operation a magnetron anode, said method comprising the steps of, in a first portion of a single stroke of the pressing operation, rearward-extruding a blank of a circular sheet of copper by means of a both opened ended female die and a male die comprising one punch formed with a plurality of radially and axially extending grooves and the other punch formed with the same grooves as said one punch, to form a semifinished article having a cylindrical peripheral wall with a plurality of thin-walled portions on its inner surface corresponding to the grooves of said male punch and a thin bottom wall connected with one end of said peripheral wall and integrally with said thin-walled portions, and, in a second portion of the single stroke of the pressing operation, subjecting said bottom wall to a precise shearing to cause the same to be punched out of said semifinished article whereby said semifinished article is punched out, being sandwiched between said one punch and said other punch in succession to said rearward-extruding step in the single stroke of the pressing operation.
 3. A method of manufacturing by a pressing operation an article having a cylindrical peripheral wall and integral thin-walled portions inwardly thereof, said method comprising the steps of initially driving a punch means in a first direction against a blank of circular sheet material arranged in die means to rearwardly extrude the blank and form a semifinished article having a cylindrical peripheral wall with a plurality of thin-walled portions on its inner surface and a thin bottom wall integrally connected with the peripheral wall and the thin-walled portions, and then driving the punch means in the first direction against the semifinished article for subjecting the bottom wall to shearing and punching the bottom wall from the semifinished article such that a finished article having a peripheral wall and integral thin-walled portions inwardly thereof is formed in a single stroke of the pressing operation. 